The present invention relates to a method and an apparatus for the conversion of organic solid waste into humic products.
More specifically, the present invention relates to a process for converting solid organic waste into humic products useful in the pedological restoration of agricultural soils.
A review of the state of health of agricultural soils currently forces the need to produce compounds which are capable of restoring the characteristics required for their use.
The indiscriminate use of pesticides, herbicides, fungicides, plant protection products, intensive single-crop farming and forcedly inorganic fertilizations in fact endanger what is known in agriculture as the xe2x80x9cagronomic health of soilsxe2x80x9d.
This negative trend is partly caused by the disappearance of rotation of crops and by the ever-decreasing availability of manure as amendment.
Furthermore, the chemicals used in agriculture have contributed to the degradation of soils to such a radical extent that the use of manure alone as amendment is no longer sufficient.
While manure is an excellent organic addition in a biologically healthy soil, in current conditions and most of all due to the lack of microorganisms which are decisive in humification-dehumification processes, its introduction leads to a residue of organic substances which cannot be metabolized and therefore to an accumulation of products which imbalance the organic C/N/P ratios.
Although manure release nitrogen which can be quickly assimilated, the slow kinetics of organic phosphor and a shortage in the soil of important pectin- and cellulose-lysing bacteria leads to infestation by seeds that were not digested by the animals and are found substantially intact in the manure.
One of the proposed solutions for dealing with this situation is the use of compost; however, in addition to biological anomalies, compost has shortcomings on an agricultural level, such as:
1. unbalanced C/N ratio;
2. the presence of nondegraded seeds which accordingly infest the cultivations for which the compost is designed;
3. the presence of nondegraded macromolecules, owing to the absence, in the epiphytic microflora, of microorganisms of the humification process;
4. a substantial modification of mineral colloids, with an increase in sodium silicates and consequent loss of the flocculating power of the soil and conversion of said soil into a silty compact soil which can be washed away and allows limited water penetration;
5. an increase in toughness, difficulty in tilling, compression of the surface layer and therefore compactness even in deep layers (below 25-30 cm).
In such conditions, humus becomes considerably important, since from the chemical-agricultural point of view its richness in nitrogen makes it an important element for treating agricultural soils; furthermore, above all the protective flocculating action that humic acids have on inorganic colloids is important, favorably modifying the toughness, porosity, permeability, aeration and water-holding capacity of the soil and accordingly improving what is known in agriculture as the xe2x80x9cagronomic healthxe2x80x9d of the soil.
In order to better comprehend the nature of the humic product that can be obtained with the method according to the present invention, it is noted that the common characteristics of various types of humic extracts of various origin can be summarized as follows:
1. a polypeptide structure bonded to lignin and containing microelements such as calcium, magnesium, zinc and aluminum;
2. a well-defined microbial range in a balanced ratio in which bacteria predominate with precise qualitative and quantitative ratios with hyphomycetes, zygosaccharomycetes, algae and protozoa;
3. the presence of fatty acids, plant hormones, phosphorylated compounds, amino acids, vitamins etcetera is closely dependent on the overall anabolic and catabolic metabolic process of the microbial mass of the core of the humus.
In order to obtain a good humus, the necessary biological operations are substantially as follows:
tyndallization. This operation tends to activate, by a microbiological pathway, the thermophilic epiphytic biomasses so that their exothermic activity leads to a temperature increase which is used to destroy parasites, their eggs and microbial sporae (these last only in particular conditions);
preparation of the basic precursor on which the characteristic biomasses of the humic core are to be seeded;
selective metabolization of certain bacterial strains. This metabolization consists in biofermentations which are performed in order to prepare:
components of the humic group (fulvic acid, crenic and apocrenic acid, sacculmic acid, etcetera)
microorganisms typical of mycorrhizae
plant hormones
microorganisms against plant infections and for soil decontamination.
A humus adapted for a pedological restoration treatment can be characterized by means of the following properties:
the essential component is a lignin proteinate of a metal, preferably magnesium;
the C/N ratio must oscillate between 9 and 12;
the nitrogen must be spread in a balanced manner between quick-assimilation nitrogen (ammoniacal N), medium-assimilation nitrogen (amide N) and slow-assimilation nitrogen (protein N).
Conventional processes for converting organic waste into humic products have turned out to be disadvantageous owing to the large number of stages and to their discontinuous operation linked to high energy costs and operating times.
One of the aims of the present invention is to provide a method and an apparatus which allow to produce a humic product which is adapted for pedological conversion and restoration of agricultural soils.
An object of the present invention is to provide a method of the above type whose initial material is constituted by waste products which are otherwise difficult to dispose of from the ecological point of view, such as for example waste from zootechnical farms, agri-foodstuff industries, or MSW.
Another object of the present invention is to provide a method and an apparatus which operate continuously shorter times and lower energy costs.
This aim, these objects and others which will become apparent hereinafter are achieved by a method for converting organic solid waste into humic products, comprising a preliminary aerobic fermentation of the material to be processed and a second aerobic fermentation of said material in the presence of specific microorganisms in order to provide a basic precursor on which the selective metabolization occurs of specific bacterial strains to provide the humic product.